Ajoene, a Stable Garlic By-Product, Has an Antioxidant Effect through Nrf2-Mediated Glutamate-Cysteine Ligase Induction in HepG2 Cells and Primary Hepatocytes

Abstract

Cytoprotective effects of chemopreventive agents may be attributed to the induction of antioxidant enzymes. Among these, the induction of glutamate-cysteine ligase (GCL) protects cells from oxidative injury by increasing glutathione (GSH) content. Nuclear factor erythroid-2-related factor 2 (Nrf2) transcriptionally regulates the expression of genes encoding for GCL and other cysteine-metabolizing enzymes. Despite extensive studies on the components in garlic, little information is available on organosulfur by-products made from garlic. In this study, we investigated whether ajoene, a chemically stable garlic by-product, has the ability to activate Nrf2 and induce GCL, and, if so, what is the role of activating Nrf2 in cytoprotection against oxidative stress. Immunoblottings and reporter gene assays were performed in HepG2 cells. Ajoene treatment activated Nrf2, as indicated by increased phosphorylation and nuclear accumulation of Nrf2, decreased interaction with Kelch-like ECH-associated protein-1, and decreased Nrf2 ubiquitination. Consistently, treatment of ajoene increased antioxidant response element reporter gene activity and the mRNA and protein levels of GCL subunits. Ajoene activated protein kinase C-delta (PKCdelta). Inhibition of PKCdelta activation by rottlerin abrogated its ability to activate Nrf2 and induce GCL, suggesting that ajoene promotes the Nrf2-dependent antioxidant defense system via PKCdelta activation. Consequently, ajoene prevented cell death, GSH depletion, and hydrogen peroxide production elicited by tert-butylhydroperoxide. The important role of Nrf2 in cytoprotection was verified by the reversal of ajoene's ability to protect hepatocytes in Nrf2-knockout mice. Our results demonstrate that ajoene increases PKCdelta-dependent Nrf2 activation, GCL induction, and the cellular GSH concentration, which may contribute to protecting cells from oxidative stress.

Stability and extraction of bioactive sulfur compounds from Allium genus processed by traditional and innovative technologies

“…This subsequently leads to the biosynthesis of various health-promoting OSCs (Abuajah et al, 2015), includingas diallyl and allyl sulfides, dithiins, and ajoene accompanied by characteristic odour (Block, 1985;Kay et al, 2010). In garlic, more than 70% of lysed thiosulfinates is comprised of allicin (diallyl thiosulfinate) which is further degraded to di-and tri-sulphides (Ramirez et al, 2017).…”

Separation of the Antioxidant Compound Quercitrin fromLindera obtusilobaBlume and Its Antimelanogenic Effect on B16F10 Melanoma Cells

“…t-BHP induces radical stress, and is used as a good experimental tool to mimic the conditions of oxidative stress. 13) Further fractionization of the LOE led to the identification of the most hepatoprotective LOE fraction against t-BHP-induced cytotoxicity (Fig. 1).…”

Saeng-Kankunbi-Tang (生肝健脾汤) protects liver against oxidative damage through activation of ERK/Nrf2 pathway

“…(15) HepG2 cells (1×10 7 ) in dishes were washed twice with ice-cold PBS and then scraped from the dishes with 1 mL of PBS and transferred to microtubes. Cells were then centrifuged at 2,000×g for 5 min.…”